In this essay, I criticize Laudan's view that methodological rules in science are best understood as hypothetical imperatives, for example, to realize cognitive aim A, follow method B. I criticize his idea that such rules are best evaluated by a naturalized philosophy of science which collects the empirical evidence bearing on the soundness of these rules. My claim is that this view yields a poor explanation of (1) the role of methodological rules in establishing the rationality of scientific practices, (2) the debates scientists have over rival methodological rules, and (3) the reasons on the basis of which scientists actually embrace, challenge, or transform methodological rules. A better explanation is provided by treating at least some methodological rules as foundational standards of theory-appraisal which define the criteria of scientific truth, knowledge, evidence, proof, explanations, etc., for a certain tradition or community of scientific practice. Such standards are in turn grounded or challenged on the basis of their coherence or incoherence with a wider body of scientific judgments. This view leads away from a naturalized philosophy of science back to its more classical epistemological conception